The mayor has every right to attack dung-flecked art -- except the right to sanction a museum showing it. As if such particulars ever mattered to the Scarpia of City Hall.

The mayor, once famous as a defender of morality and order, has surely gone over to the cause of indecency and relativism. How else to explain his actions over the past two weeks, which have served chiefly to galvanize much of the city's cultural elite behind an exhibit most of its members were inclined to dismiss as overhyped commercialism and to force untold numbers of Clinton-fatigued liberals to begin to view Mrs. C in a new -- and altogether more favorable -- light?

It's hard to see what else his latest crusade has accomplished. He'll likely lose the upcoming court battle with the Brooklyn Museum over the "Sensation" exhibit scheduled to open last Saturday. But he won't stop there, because he never stops. Wonder what he'll try to do to the Brooklyn Museum during the next budget season (the First Amendment makes no claim on budgets). Or what kind of pressure will be brought to bear on the museum's trustees with respect to the tenure of the unfortunate Mr. Lehman. Rudy never forgets.

If there's one thing we should know by now about Giuliani when it comes to this kind of flare-up, it's that while there's some political calculus to what he does, you cannot deny that, at bottom, he believes he's right. You have to admire that. In a way. For about five seconds. But then you start realizing that you're seeing the mayor, one more outrageous time, using his office for another personal jihad. He believed it, too, when he thought he was going to plant a homeless shelter in Brooklyn councilman Steve DiBrienza's district just because DiBrienza had had the gall to throw the social-welfare-policy equivalent of elephant dung on the mayor's homeless policy. And he meant it, too, when he decided that Calvin Butts had knocked him once too often and once too crudely, and went back on a city promise of land for a shopping development on West 125th Street because Butts's Abyssinian Development Corporation is leading the project.

The conventional thinking on Giuliani has gone as follows: first term, great mayor, should cool it some; early second term, still a good mayor, done a lot for the city, but really ought to try to be nicer. In other words: It's always been accepted wisdom to say that he's been a good mayor but his inquisitorial personality has been a little bit of a problem.

Well, his personality has become more than a little bit of a problem. Separating his governance from his personality is now a logical fallacy. His personality has become municipal government. Now that he's basically run out of issues, not proposing any striking new initiatives, pursuing a campaign which demands that he alienate two thirds of his city as he panders to national conservative money (and this is central to what the Brooklyn Museum fracas is about in political terms: his fund-raising's not going as well as expected, and the national headlines should deliver a hefty cash infusion from the right), his administration is entirely about his personality. His mayoralty and his ego and his ambition have all become one and the same. The only thing he's done for the past year, year and a half, is pick fights. DiBrienza. Butts. Rudy Crew, on vouchers. Mark Green, on mayoral succession. Pedestrians, over equal access to 49th and 50th Streets. An overhyped exhibit that few in the art world want to defend.

Or, rather, that few wanted to defend. But lo and behold, after a week of timorous silence, the cultural elite finally snapped to attention. The letter 26 cultural leaders sent to the mayor last week was tamer than tame (it began: "In view of how consistently enlightened and generous both you and the City Council have been in supporting the arts in recent years . . ."), a rhetorical keepsake of the instrumental fear with which Giuliani has increasingly governed; but at least they said something. Compare them with Schuyler Chapin, the city's cultural-affairs commissioner, who cravenly refused to get involved in the controversy. Chapin, who distinguished himself as general manager of the mayor's beloved Metropolitan Opera and head of Columbia's arts school, should have stood up to his bully boss by immediately tendering his resignation from a job he does not need.

Yeah, but what about the work itself, you say? Well, it's sacrilegious. So is lots of other good art, and bad art. It'll be remembered or forgotten as it deserves. But Giuliani had several time-honored and thoroughly American tools of censure at his disposal -- speech, leading a boycott, appealing in a measured way to the Brooklyn Museum's sense of respect for the community -- short of yanking the museum's funding. That's against the law and virtually every precedent set by every court in the country. It may mean we have to tolerate some offense, but it's what keeps the censorious from clearing out America's library shelves and museum walls.

And as for the Senate race: Giuliani's gambit looks on the surface like a clever solidifying of his base vote, and undoubtedly it does him some good there. But overall, it's bad politics. Everybody who supports what he's doing is voting for him anyway, but the election will be decided by about 200,000 voters who are in the center and who may have more sophisticated views about free speech and culture than tabloid headline-writers and pollsters give them credit for.

There is one unswervable truth about New York elections, which is that their outcomes coincide -- always -- with the voting patterns of liberal-to-moderate yuppies. Giuliani should know this better than anyone, since they were against him in 1989 when he lost, kinda for him in 1993 when he won, strongly for him in 1997 when he steamrolled. Those were city elections, but the same has been true of state elections as well. Mario Cuomo lost to George Pataki in 1994, when they were a little tired of the governor and didn't turn out; Chuck Schumer beat Al D'Amato in 1998, when they did turn out for the congressman. Direct cause and effect? Maybe, maybe not, but it somehow always seems to work out that way. One senses that few of these voters -- who vote in higher numbers than Reagan-Democrat Catholics -- have been impressed by the mayor's cavils.

Charles Saatchi, who once created Margaret Thatcher's ads, is probably not likely to write a check to Hillary. But she might end up with reason to thank him.